MSL3088-IUR Atmel, MSL3088-IUR Datasheet - Page 19

• Manufacturer Part Number: MSL3088-IUR
• Description: LED Lighting Drivers 8-Str LED Driver Intrnl Bst Cntr/Phas
• Manufacturer: Atmel

Specifications of MSL3088-IUR

• Rohs: yes
• Input Voltage: 5 V
• Operating Frequency: 200 Hz
• Maximum Supply Current: 18 mA
• Output Current: 350 uA
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Package / Case: VQFN-24
• Minimum Operating Temperature: - 40 C
• Power Dissipation: 1850 mW

9.7 Setting the Boost Regulator Output Voltage
9.8 Choosing the Input and output Capacitors
9.9 Choosing the Inductor
Select the voltage divider resistors (R
and maximum LED string anode power supply (boost regulator) voltage, using:
where V
For example, if the LED minimum forward voltage is V
minimum and maximum voltage drop across a string is 35V and 38V. Adding allowance of 0.5V for the current regulator headroom brings
V
The input and output capacitors carry the high frequency current due to the boost regulator switching. The input capacitor prevents this
high frequency current from travelling back to the input voltage source, reducing conducted and radiated noise. The output capacitor
prevents high frequency current to the load, in this case the LEDs, and also prevents conducted and radiated noise. The output
capacitors also have a large effect on the boost regulator loop stability and transient response, and so are critical to optimal boost
regulator operation.
Use ceramic input and output capacitors that keep their rated capacitance values at the expected operating voltages. The “Typical
Application Circuit” on page 11 shows recommended values for and 10 LEDs and 60mA per string. Use a bulk electrolytic capacitor
where power enters the circuit board.
The boost regulator inductor takes the current from the input source and directs that current to the load. Using the proper inductor is
critical to proper boost regulator operation. Choose an inductor with sufficient inductance to keep the inductor ripple current within limits,
and with sufficient current handling capability for steady-state and transient conditions.
The boost regulator switching causes ripple current through the inductor. The current rises during the on-time and falls during the off time.
The slope of the inductor current is a function of the voltage across the inductor, and so the total change in current, Δ
slope multiplied by the time in that phase (on time, t
voltage are all constant, the inductor current does not change over one cycle, and so the amount the current rises during the on time
is the same as the amount the current drops during the off time. Calculate the duty cycle (equal to the on-time divided by the switching
period) using:
where V
where f
where L is the inductance value in Henrys. Choose a value for L that produces a ripple current in the range of 25% to 50% of the steady
state DC inductor current. The steady state DC inductor current is equal to the input current. Estimate the steady-state DC input current
using:
where I
boost regulator output voltage, and VIN is the minimum boost regulator input voltage.
Then determine R
C
The input and output capacitors carry the high frequency current due to the boost regulator switching. The input capac
prevents this high frequency current from travelling back to the input voltage source, reducing conducted and radiated
noise. The output capacitor prevents high frequency current to the load, in this case the LEDs, and also prevents
conducted and radiated noise. The output capacitors also have a large effect on the boost regulator loop stability and
transient response, and so are critical to optimal boost regulator operation.
C
Use ceramic input and output capacitors that keep their rated capacitance values at the expected operating voltages. T
Typical Application Circuit on page 11 shows recommended values for and 10 LEDs and 60mA per string. Use a bulk
electrolytic capacitor where power enters the circuit board.
C
The boost regulator inductor takes the current from the input source and directs that current to the load. Using the prop
inductor is critical to proper boost regulator operation. Choose an inductor with sufficient inductance to keep the induct
ripple current within limits, and with sufficient current handling capability for steady-state and transient conditions.
The boost regulator switching causes ripple current through the inductor. The current rises during the on-time and falls
during the off time. The slope of the inductor current is a function of the voltage across the inductor, and so the total
change in current, ∆I
state, where the load current, input voltage, and output voltage are all constant, the inductor current does not change o
one cycle, and so the amount the current rises during the on time is the same as the amount the current drops during t
off time. Calculate the duty cycle (equal to the on-time divided by the switching period) using:
where V
where f
Calculate the on-time in seconds using:
Calculate the inductor ripple current using:
©
where L is the inductance value in Henrys. Choose a value for L that produces a ripple current in the range of 25% to 5
of the steady state DC inductor current. The steady state DC inductor current is equal to the input current. Estimate the
steady-state DC input current using:
where I
optimized) boost regulator output voltage, and V
Inductors have two types of maximum current ratings, RMS current and saturation current. Make sure that the peak
inductor current is less than the saturation current rating. Note that during load current transients, which occur whenev
the LEDs are turned on or off (due to PWM dimming), the inductor current may overshoot its steady state value. How
t
R
R
D
I
OUT(MIN)
ON
IN
HOOSING THE
HOOSING THE
HOOSING THE
Atmel Inc., 2011. All rights reserved.
TOP
I

BOTTOM

L

V

Figure 5. Efficiency Optimizer (EO)
S
Select the voltage divider resistors (R
the minimum and maximum LED string anode power supply (boost regulator) voltage, using:
©
SW
LOAD
V

f(MIN)
OUT
OUT
I
to 35.5V and V
ETTING THE
OUT
SW
LOAD
Atmel Inc., 2011. All rights reserved.
V
f
is the boost regulator switching frequency. Calculate the inductor ripple current using:
LOAD
D
OUT
V
SW
V
is the output voltage and V
IN
is the sum of all strings steady-state LED currents with all LEDs on simultaneously, V
OUT
and V
is the boost regulator switching frequency.
IN
(

MIN
L
is the output voltage and V
is the sum of all strings steady-state LED currents with all LEDs on simultaneously, V
R
V

(
TOP
t
MAX
365
)
IN
V
ON
f(MAX)
V



V
OUT
OUT
V
,

I
I
I
)
OUT
BOTTOM

NPUT AND
NPUT AND
NDUCTOR

IN
V
OUT(MAX)

are the LED’s minimum and maximum forward voltage drops at the full-scale current set by R
V
10
B
f
V
V
V
L
OUT
(
, is the current slope multiplied by the time in that phase (on time, t



MIN
OUT
OUT
IN
OOST
V
6
f
,
SW
IN
(MAX
using:
V
)
to 38.5. Next determine R
(
2

OUT
MIN
5 .
,

)
#
f
R
TOP
)
O
O

SW
IN
ofLEDs

EGULATOR
UTPUT
UTPUT
2
and R
is the input voltage. Calculate the on-time in seconds using:
V
5 .
.
IN
MSL3086/MSL3087/MSL3088 Datashee
L

BOTTOM
,
.
IN

C
C

ON
is the input voltage.

APACITORS
APACITORS
, or off time, t
f(MIN)
TOP
in Figure 8.1 on page 13) by first determining V
0
OUT(MIN)
O
5 .
UTPUT
TOP
and R
, and
= 3.5V and maximum is V
Then determine
IN
R
8-String 60mA LED Drivers with Integrated Boost Controller and Phase Shifted Dimming
using:
BOTTOM
is the minimum boost regulator input voltage.
BOTTOM
OFF
and
V
Page 20 of 26
OLTAGE
using:
). In steady-state, where the load current, input voltage, and output
in Figure 3 on page 12) by first determining V
Page 17 of 22

where V
(page 14). For example, if the LED minimum forward vo
LEDs in a string, the total minimum and maximum voltag
for the current regulator headroom brings V
Then determine R
C
The input and output capacitors carry the high frequency
prevents this high frequency current from travelling back
noise. The output capacitor prevents high frequency cur
conducted and radiated noise. The output capacitors als
transient response, and so are critical to optimal boost r
C
Use ceramic input and output capacitors that keep their
Typical Application Circuit on page 10 shows recommen
electrolytic capacitor where power enters the circuit boa
C
The boost regulator inductor takes the current from the i
inductor is critical to proper boost regulator operation. C
ripple current within limits, and with sufficient current ha
The boost regulator switching causes ripple current thro
during the off time. The slope of the inductor current is a
change in current, ∆I
state, where the load current, input voltage, and output v
one cycle, and so the amount the current rises during th
off time. Calculate the duty cycle (equal to the on-time d
where V
Calculate the on-time in seconds using:
V
t
R
R
D
ON
OUT
TOP
HOOSING THE
HOOSING THE
HOOSING THE
BOTTOM


OUT(MAX)


where V
(page 15). For example, if the LED minimum forward
LEDs in a string, the total minimum and maximum vo
for the current regulator headroom brings V
Then determine R
C
The input and output capacitors carry the high freque
prevents this high frequency current from travelling b
noise. The output capacitor prevents high frequency
conducted and radiated noise. The output capacitors
transient response, and so are critical to optimal boo
C
Use ceramic input and output capacitors that keep th
Typical Application Circuit on page 11 shows recomm
electrolytic capacitor where power enters the circuit
C
The boost regulator inductor takes the current from t
inductor is critical to proper boost regulator operation
ripple current within limits, and with sufficient current
The boost regulator switching causes ripple current t
during the off time. The slope of the inductor current
change in current, ∆I
state, where the load current, input voltage, and outp
one cycle, and so the amount the current rises durin
off time. Calculate the duty cycle (equal to the on-tim
where V
Calculate the on-time in seconds using:
©
V
V
R
R
D

(
f(MAX)
V
OUT
OUT
HOOSING THE
HOOSING THE
HOOSING THE
TOP
Atmel Inc., 2011. All rights reserved.

BOTTOM
MAX
Atmel MSL3086/MSL3088 Datasheet


OUT
f
f(MIN)
OUT
D
V
SW
(
(
V
V
MIN
MAX
)

= 3.8V, using 10 LEDs in a string, the total
OUT
OUT
IN

f(MIN)
V
OUT
is the output voltage and V
R

)
V
V
and V
)

(
OUT
V
TOP
MAX
365
IN
IN
V

V
OUT
is the output voltage and V
f
R
OUT

V
and V
V
(
IN

(
,
V
MAX
TOP

I
I
I
MAX
365
)
BOTTOM
IN
is the maximum (un-optimized)
NPUT AND
NPUT AND
NDUCTOR

f
OUT(MIN)
f(MAX)


f
V
(
MIN
(
10

,
L
MAX
)
V

I
OUT
I
I
)
BOTTOM
, is the current slope multiplied by
f
NPUT AND
NPUT AND
NDUCTOR

V

f(MAX)
OUT

SW
V
6
)
10
IN

are the LED’s minimum and ma
)
L
V
(MAX

#
OUT
and V
using:
, is the current slope multiplied

ON
(
2
OUT

ofLEDs
6
,
MIN
#
5 .

are the LED’s minimum and
(MAX
, or off time, t
#
using:
)
ofLEDs
2
OUT(MAX)
(
)
ofLEDs
O
O
MIN

IL
5 .

ILED
, is the current
UTPUT
UTPUT
2
)
)
O
5 .
O
.

OUT


(page 16).

UTPUT
UTPUT
, the minimum
2


TOP
5 .

.


is the maximum (
0
.
IN



C
C
5 .

is the input volt
0
OFF
APACITORS
APACITORS
.
0
IN
5 .
,
OUT(MIN)
OUT(MIN)
C
C
5 .
). In steady
19
is the input
, and
APACITOR
APACITOR
,
OUT(MIN)
and V
to 35
to